JP4997421B2 - Method for producing visible light responsive photocatalyst - Google Patents

Description

  The present invention relates to a method for producing a visible light responsive photocatalyst.

  Conventionally, a photocatalyst has attracted attention from the viewpoint of environmental purification. A photocatalyst is one that decomposes harmful substances such as organic compounds and bacteria that come into contact with light by generating strong oxidizing power on its surface. Among such photocatalysts, titanium oxide can be cited as a substance having an excellent catalytic function.

  Pure titanium oxide functions as a photocatalyst only by irradiation with ultraviolet light, does not respond to irradiation with visible light other than the ultraviolet light region, and cannot exert a catalytic function. For this reason, pure titanium oxide does not respond to the light of a fluorescent lamp indoors or in a vehicle and cannot be purified.

  In order to eliminate such inconveniences, in recent years, research on visible light responsive photocatalysts has been widely performed (for example, see Patent Documents 1 to 3).

JP 2001-205103 A JP 2004-49969 A Japanese Patent No. 3498739

In Patent Document 1, a TiO ₂ thin film that is titanium oxide is processed in a vacuum chamber into which nitrogen gas and an inert gas are introduced, so that a part of oxygen in the TiO ₂ thin film crystal is replaced with nitrogen, and Ti A method of forming an —O—N structure is described. When a part of the structure of TiO ₂ is substituted with nitrogen in this manner, it becomes a visible light responsive photocatalyst and can be used indoors.

  Patent Document 2 describes a method of forming a Ti—O—N structure using titanium tetrachloride as a raw material, and more specifically, by burning a mixed gas of titanium tetrachloride and oxygen in the gas phase. A method for producing titanium oxide having a Ti—O—N structure by hydrolyzing titanium tetrachloride is described.

  Patent Document 3 describes a method of manufacturing titanium oxide having a Ti—O—N structure by heat-treating titanium oxide in an atmosphere containing ammonia gas.

  Thus, a visible light responsive photocatalyst can be obtained by using titanium oxide having a structure having a Ti—O—N structure. However, the conventional visible light responsive photocatalyst manufacturing method described above has the following problems.

That is, in the method described in Patent Document 1, it is necessary to perform heat treatment at a high temperature of 550 ° C. after forming a Ti—O—N film on the surface of TiO ₂ . In addition, in the method described in Patent Document 2, a small amount of chloride may be attached to the manufactured titanium chloride, and in order to remove the attached chloride, the temperature is from 300 ° C to 500 ° C. It is necessary to perform heat treatment at temperature. In the method described in Patent Document 3, it is necessary to heat-treat titanium oxide at a temperature of 400 ° C. to 700 ° C.

  Thus, according to the conventional technique, the titanium oxide is exposed to a high temperature. And after cooling titanium oxide, a product is finally produced by processing this titanium oxide and attaching it to the product. Here, it is generally preferable that the manufacturing process is an efficient operation. In this case, after attaching the titanium oxide before the treatment to the product, the titanium oxide is treated for each product, and then the product is cooled. It is an efficient work to do. However, when a low-melting-point material such as plastic is used for the product, since the plastic or the like melts, there is a problem that a series of operations as described above cannot be performed and workability is deteriorated. . In addition, since the titanium oxide is exposed to a high temperature, there is a problem that energy required for the treatment is increased and energy efficiency is poor.

  In addition, since a gas other than oxygen and nitrogen is used, there is a possibility that a highly pure Ti—O—N composition cannot be obtained. These problems will be a serious adverse effect in the practical application of products.

  The present invention has been made in view of the above, and provides a method for producing a visible light responsive photocatalyst capable of producing a visible light responsive photocatalyst in a low temperature region and capable of obtaining a high quality photocatalyst. The purpose is to provide.

To achieve the above object, a manufacturing method of a visible light-responsive photocatalyst according to claim 1 is a method for producing a visible light responsive photocatalyst in response to irradiation with visible light causing photocatalytic reaction, nitrogen A plasma nitriding process is performed on the titanium material in an atmosphere of gas and nitrogen oxide, and the temperature of the titanium material is maintained at 100 ° C. to 300 ° C. during the plasma nitriding process.

  That is, in the invention according to claim 1, since the titanium material is plasma-nitrided in a nitrogen oxide atmosphere, a high-purity Ti—O—N composition can be obtained, and thus a high-quality photocatalyst is manufactured. be able to.

Further, since the temperature of the titanium material is maintained at 100 ° C. to 300 ° C. during the plasma nitriding treatment, a series of operations can be performed even when a product is manufactured using the titanium material. For example, even if a low-melting-point material such as plastic is used for the product, since the entire product can be processed after the titanium material is attached to the product, an efficient operation can be performed. Further, since the temperature of the titanium material is kept low, the energy used can be reduced. The conventional method for producing a visible light responsive photocatalyst cannot obtain the above-described advantages because the temperature of the object to be processed is in a high temperature region of 300 ° C. or higher and there is no viewpoint of making it a low temperature region. It was. Therefore, it is possible to produce a high-quality photocatalyst while improving such a point by keeping the temperature of the titanium material at a low temperature.
In the plasma nitriding treatment, the temperature of titanium is preferably maintained at 150 ° C. to 250 ° C., and more preferably, the temperature of titanium is maintained at around 200 ° C.

The method for producing a visible light responsive photocatalyst according to claim 2 is the method for producing a visible light responsive photocatalyst according to claim 1, wherein the nitrogen oxide is nitrogen dioxide, nitric oxide or nitrous oxide. It is either of these .

That is, the invention according to claim 2 can perform the plasma nitriding treatment on the titanium material under efficient conditions.
The nitrogen oxide atmosphere is more preferably nitrogen dioxide.

  Further, the method for producing a visible light responsive photocatalyst according to claim 3 is the method for producing a visible light responsive photocatalyst according to claim 1 or 2, wherein the plasma nitriding treatment is performed in a vacuum furnace having a pressure of 150 Pa to 250 Pa. The titanium material is held on the surface, the voltage of 550 V to 650 V is applied between the titanium material and the vacuum furnace, and the temperature of the titanium material is maintained at 100 ° C. to 300 ° C. by repeatedly turning on / off the power source. It is characterized by.

That is, the invention according to claim 3 can perform the plasma nitriding process on the titanium material under more efficient conditions.
In the plasma nitriding treatment, the titanium material is held in a vacuum furnace at a pressure of 200 Pa, a voltage of 590 V is applied between the titanium material and the vacuum furnace, and the temperature of the titanium material is changed by repeatedly turning on / off the power. More preferably, it is kept at 200 ° C.

  As described above, according to the present invention (claim 1), a high-quality photocatalyst can be produced while producing a visible light responsive photocatalyst in a low temperature region. According to the present invention (claim 2), the plasma nitriding treatment can be performed on the titanium material under efficient conditions. Further, according to the present invention (claim 3), the plasma nitriding treatment can be performed on the titanium material under more efficient conditions.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram schematically showing a configuration of a production apparatus for carrying out a method for producing a visible light responsive photocatalyst according to an embodiment of the present invention.

The manufacturing apparatus 1 is an apparatus for performing a plasma nitriding process on an object to be processed, and includes a vacuum chamber 2, a gas supply unit 3, a plasma power source 4, and an exhaust pipe 5.
The vacuum chamber 2 includes a vacuum tube 21 for keeping the inside at a predetermined pressure, a base 22 provided in the vacuum tube 21, a pressure adjusting unit 23 for adjusting the pressure in the vacuum chamber 2, And a temperature adjusting unit 24 for adjusting the temperature of the object to be processed.

The vacuum tube 21 functions as an anode side electrode.
The base 22 functions as an electrode on the cathode side, and is used for placing an object to be processed on the upper surface.
The pressure adjusting unit 23 controls the operation of the gas supply unit 3 to keep the inside of the vacuum tube 21 at a predetermined pressure.
The temperature adjustment unit 24 detects the temperature of the object to be processed placed on the base 22 as needed, and controls the operation of the plasma power source 4 described later.

The gas supply unit 3 keeps the gas concentration in the vacuum chamber 2 at a predetermined concentration while supplying a predetermined gas into the vacuum chamber 2 in accordance with the control of the pressure adjusting unit 23, and at the same time, keeps the inside of the vacuum chamber 2 at a predetermined level. Is to keep the pressure of
The plasma power supply 4 generates a glow discharge in the vacuum chamber 2 by applying a predetermined voltage between the vacuum tube 21 and the base 22.
The exhaust pipe 5 is for exhausting the gas in the vacuum chamber 2 to make a vacuum, and can be opened and closed by a cock (not shown). Usually, the cock of the exhaust pipe 5 is closed, and the vacuum chamber 2 is sealed.

  Then, when using the manufacturing apparatus 1, first, an object to be processed is placed on the base 22, and the vacuum chamber 2 is kept in vacuum by the exhaust pipe 5. Then, a predetermined gas is supplied from the gas supply unit 3 into the vacuum chamber 2. At this time, the pressure adjusting unit 23 controls the operation of the gas supply unit 3 to keep the pressure in the vacuum chamber 2 constant.

  Next, a predetermined voltage is applied to the vacuum tube 21 and the base 22 by the plasma power source 4 to generate glow discharge in the vacuum tube 21. At this time, the temperature adjusting unit 24 detects the temperature of the object to be processed on the base 22 and repeats turning on / off of the plasma power source 4 so that the temperature of the object to be processed becomes constant. After glow discharge is performed for a predetermined time, the inside of the vacuum chamber 2 is again kept in vacuum by the exhaust pipe 5 to cool the object to be processed. In this way, the plasma nitriding process is performed on the object to be processed.

  In the following examples, a nitrogen oxide atmosphere was supplied into the vacuum chamber 2 and a titanium substrate (Ti substrate) was used as an object to be processed. Further, the plasma nitriding treatment was performed by variously changing the type of gas supplied into the vacuum chamber 2, the concentration of the gas, and the temperature of the object to be processed. Moreover, the Ti substrate was plasma-nitrided using the industrial metal surface treatment apparatus (manufactured by San-in Oxygen Co., Ltd.) as the production apparatus 1, and the performance of the photocatalyst of the treated Ti substrate was examined.

Example 1
A Ti substrate (20 × 20 mm) is placed on the base 22, nitrogen dioxide (NO ₂ ) is supplied into the vacuum chamber 2, and its concentration is kept at 33% using nitrogen gas (N ₂ ) as a dilution gas. It was. The pressure in the vacuum chamber 2 was 200 Pa. And what performed plasma nitriding treatment with the temperature of the Ti substrate being 100 ° C., what was plasma nitriding treatment at 150 ° C., what was plasma nitriding treatment at 200 ° C., and what was plasma nitriding treatment at 250 ° C. Six types were prepared: those subjected to plasma nitriding treatment at 300 ° C. and those subjected to plasma nitriding treatment at 550 ° C. Each plasma nitriding treatment was performed for 3 hours.

And in order to investigate the absorption wavelength range of the Ti substrate after a process (henceforth a sample), the light absorption was investigated using the ultraviolet visible spectrophotometer (JASCO V-550 type). The measurement conditions were a bandwidth (UV) of 0.1 nm, a measurement wavelength of 200 nm to 800 nm, a data interval of 0.5 nm, and a scanning speed of 20 nm / min. A graph of the results is shown in FIG.
From this graph, it can be confirmed that the absorption edge of the spectrum is shifted to the long wavelength side as the production temperature rises for each sample. In addition, it can be confirmed that light having a wavelength of λ> 380 nm which is a visible light region is absorbed, and it can be confirmed that the structure has a Ti—O—N structure.

  Moreover, in order to investigate the photocatalytic performance of each sample, acetaldehyde resolution measurement was performed. Specifically, each sample is placed in a reaction layer (250 × 400 × 300 mm), and 1.4 ul of liquid acetaldehyde is volatilized in a syringe and injected into each reaction layer to be filled. It was. Each sample was irradiated with visible light for 150 minutes at a distance of 50 mm from the light source (12 V, 100 W). The amount of acetaldehyde that could be removed was defined as the removal rate, and the results are shown in FIG. From this, it was confirmed that the removal rate of the sample whose temperature was maintained at 200 ° C. was the highest. Therefore, when the Ti substrate is plasma-nitrided, the temperature of the Ti substrate is preferably 150 ° C. to 250 ° C., and more preferably 200 ° C.

(Example 2)
Nitrogen dioxide (NO ₂ ) was supplied into the vacuum chamber 2 and the concentrations thereof were set to three types of 10%, 20% and 50%, and samples were prepared in the same manner as in Experimental Example 1. The temperature of each sample was always kept at 200 ° C. In the same manner as in Experimental Example 1, the light absorption of each sample was examined, and further, acetaldehyde resolution measurement was performed. FIG. 4 shows the result of light absorption, and FIG. 5 shows the result of acetaldehyde resolution measurement.

  From FIG. 4, it can be confirmed that even if the concentration of nitrogen dioxide is changed, no significant change is observed in the absorption edge of the spectrum. Further, it can be confirmed from FIG. 5 that even if the concentration of nitrogen dioxide is changed, no significant change is observed in the acetaldehyde removal rate. Therefore, it is considered that the difference in the concentration of the nitrogen oxide atmosphere when plasma nitriding the Ti substrate does not significantly affect the quality of the photocatalyst to be produced.

(Experimental example 3)
Samples were prepared for each of three types of gases supplied into the vacuum chamber 2: nitrogen dioxide (NO ₂ ), nitrogen monoxide (NO), and nitrous oxide (N ₂ O). Further, in the case of using each gas, three types were prepared: one in which the temperature of the sample was kept at 200 ° C., one kept at 300 ° C., and one kept at 500 ° C. The concentration of each gas was kept at 33%. In the same manner as in Experimental Example 1, the light absorption of each sample was examined, and further, acetaldehyde resolution measurement was performed. In Experimental Example 3, the experiment was performed by switching between a dark condition in which no light was irradiated and a bright condition in which light in the visible light region was irradiated.

FIG. 6A is a graph showing the result of light absorption when the type of gas is nitrogen dioxide (NO ₂ ), and FIG. 6B is the case where the type of gas is nitrogen dioxide (NO ₂ ). It is the table | surface which showed the result of acetaldehyde resolution | decomposability measurement of. FIG. 7A is a graph showing the result of light absorption when the type of gas is nitric oxide (NO), and FIG. 7B is the graph showing the type of gas being nitrogen monoxide (NO). It is the table | surface which showed the result of the acetaldehyde resolution measurement in the case of. FIG. 8A is a graph showing the result of light absorption when the gas type is nitrous oxide (N ₂ 0). FIG. 8B is a graph showing the gas type being nitrous oxide (N ₂ O). N 2 ₀₎ is a table showing the results of acetaldehyde resolution measurement case.

From FIG. 6 to FIG. 8, it can be confirmed that acetaldehyde is most removed when the type of gas is nitrogen dioxide (NO ₂ ). Further, it can be confirmed that the absorption edge of the spectrum is shifted to the long wavelength side as the temperature of the sample rises. Moreover, it can be confirmed that the removal rate of the sample whose temperature is kept at 200 ° C. is the highest. Further, it can be confirmed that acetaldehyde is little removed under dark conditions, and acetaldehyde can be remarkably removed under bright conditions. Therefore, it is considered that when the Ti substrate is subjected to plasma nitriding, the treated Ti substrate is activated in response to visible light. Further, it is considered that the atmosphere is preferably nitrogen dioxide (NO ₂ ) when plasma nitriding the Ti substrate.

  The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims.

It is the figure which showed typically the structure of the manufacturing apparatus for enforcing the manufacturing method of the visible light response type photocatalyst concerning one Embodiment of this invention. 2 is a graph showing the results of Example 1. 2 is a table showing the results of Example 1. 6 is a graph showing the results of Example 2. 6 is a table showing the results of Example 2. In Example 3, it is the figure which showed the result at the time of setting the kind of gas to nitrogen dioxide. It is the figure which showed the result at the time of setting the kind of gas to nitric oxide in Example 3. It is the figure which showed the result at the time of setting the kind of gas to nitrous oxide in Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Vacuum chamber 3 Gas supply part 4 Plasma power supply 23 Pressure adjustment part 24 Temperature adjustment part

Claims (3)

A method for producing a visible light responsive photocatalyst that causes a photocatalytic reaction in response to irradiation with visible light,
Visible light response characterized in that plasma nitriding is performed on a titanium material in an atmosphere of nitrogen gas and nitrogen oxide, and the temperature of the titanium material is maintained at 100 ° C. to 300 ° C. during the plasma nitriding treatment. Type photocatalyst production method.
The method for producing a visible light responsive photocatalyst according to claim 1, wherein the nitrogen oxide is any one of nitrogen dioxide, nitric oxide, and nitrous oxide.
The plasma nitriding treatment is performed by holding a titanium material in a vacuum furnace at a pressure of 150 Pa to 250 Pa, applying a voltage of 550 V to 650 V between the titanium material and the vacuum furnace, and repeatedly turning on / off the power source. The method for producing a visible light responsive photocatalyst according to claim 1 or 2, wherein the temperature is maintained at 100 to 300 ° C.

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